The field of the present invention is that of the silicone materials comprising a polyorganosiloxane (POS for short) composition, which can be crosslinked or cured into a silicone elastomer by polyaddition reactions, and a wetting agent allowing a hydrophilic character to be conferred on the said material. The applications intended for such systems are, especially, the taking of impressions and, more particularly, the taking of dental impressions within the context of producing dentures. The expression xe2x80x9ctaking of impressionsxe2x80x9d is understood to mean, in the present text, not only the operations of taking impressions of whatever object and of whatever shape, in order to produce a model made in particular of plaster, but also the operations of reproducing or duplicating models made in particular of plaster. The expression xe2x80x9ctaking of dental impressionsxe2x80x9d is understood to mean, in the present text, not only the operations in which dental impressions are taken in the mouth in order to obtain precise copies of jaws or parts of jaws which may or may not bear, totally or partly, teeth and to form plaster models, but also the duplicating operations in which plaster models of jaws or parts of jaws are reproduced in a laboratory for dentures. The intended applications also encompass, in particular, the manufacture of pads, such as those used in pad printing techniques.
The subject of the present invention is also a process for preparing the hydrophilic silicone elastomer material. The subject of the invention is also the use of the said material for taking impressions, for example dental impressions. Finally, the subject of the invention is the use of the said material for the manufacture of pads, such as those used in pad printing techniques.
Silicone materials are widely used in these fields. This is partly due to the fact that silicone materials exhibit, on the one hand, a great diversity of chemical, mechanical and physical characteristics and, on the other hand, non-toxic, non-irritant and non-allergenic behaviour. Furthermore, silicone materials constitute poor substrates for the cultivation of microorganisms, thereby giving them remarkable properties with regard to hygiene.
The POS compositions of interest within the context of the present invention comprise at least:
a POS(1) composition carrying Si-alkenyl functional groups which are capable of reacting by addition reactions with the Sixe2x80x94H crosslinking functional groups of a POS(2) composition;
a POS(2) composition carrying Sixe2x80x94H functional groups which are capable of reacting with the Si-alkenyl functional groups of the POS(1) composition;
optionally, an unreactive POS(3) composition, differing from the POS(1) and POS(2) compositions, which can be used as a diluent;
a catalyst for catalysing the polyaddition reactions; and
a particulate reinforcing mineral filler, generally of a silicious nature, treated with a compatibilizing agent, based especially on an organosilane or on an organosilazane, and optionally a semi-reinforcing or bulking filler.
It is known that such POS compositions, which advantageously may be in the form of two components, are crosslinkable or curable at room temperature and are particularly beneficial in the field of taking impressions, in particular dental impressions, since these compositions are endowed with flow and film-forming properties before crosslinking, making it possible to take an impression of whatever shape with excellent reproduction of the details. Moreover, these compositions can crosslink by polyaddition reactions in a few minutes at room temperature; in addition, they are non-toxic and satisfy the European pharmaceutical regulations. The crosslinking, which results in the hardening of the silicone composition, makes it possible to form moulds made of elastomers having mechanical properties, dimensional stability and thermal resistance which all comply with the desired specifications.
However, compositions for impressions based on silicone crosslinking by polyaddition reactions are intrinsically hydrophobic. Thus, when the mixed moulding compound is applied to the wet surface of teeth and gums, there may therefore be a casting defect or insufficient penetration into the hollows of the gums because of the presence of liquid residues; after crosslinking, the reproduction is therefore defective. Moreover, during the operations of duplicating the positive of the plaster impression, refractory plaster of hydrophilic character has to be poured into a mould made of hydrophobic silicone; there may be occlusion of small air bubbles because of the incompatibility between the surfaces, this occlusion resulting in defective reproduction.
These drawbacks may be practically eliminated by giving the intrinsically hydrophobic POS compositions a hydrophilic character by the use of various surfactants; thus, it has been proposed to use: in U.S. Pat. No. 4,657,959, a polyorganosiloxane with polyether functional groups; in U.S. Pat. No. 4,691,039 and U.S. Pat. No. 4,752,633, an ethoxylated silane; in U.S. Pat. No. 5,064,891, a polyorganosiloxane with polyol functional groups; in EP-A-0,480,233, a poly(alkoxylated) fatty alcohol; and, in FR-A-2,600,886, a water-soluble protein combined if necessary with a nonionic surfactant.
Continuing research in this field of the art, the Applicant has found:
that the introduction of one or more surfactants into a polyaddition POS composition, containing a filler consisting, entirely or partly, of a treated reinforcing mineral filler,
results in the development of a thixotropic character, that is to say in a significant increase in the viscosity of the silicone material in the uncrosslinked state comprising, as constituent elements, the POS composition and the surfactant(s); the silicone material consequently becomes insufficiently flowable and this drawback is of the kind to cause considerable trouble in the operations of taking impressions and to degrade the quality of the reproduction of the details.
This thixotropy phenomenon, connected with the introduction of surfactant(s) into the POS compositions with treated reinforcing mineral fillers, manifests itself particularly adversely in the case of silicone materials whose content of treated reinforcing mineral filler is high, for example equal to or greater than about 15% with respect to the weight of the silicone material. This limit of about 15% can be lowered to about 10% when the silicone material also includes a semi-reinforcing or bulking filler in an amount of 10% to 30% with respect to the weight of the silicone material.
It has now been found that it is possible to get round this difficulty by using, for preparing the silicone material, a particular treated reinforcing mineral filler, which is in the form of a suspension obtained by carrying out a two-stage treatment of the filler with a compatibilizing agent (CA for short) and by performing this treatment in the presence of at least one portion of the POS(1) composition carrying Si-alkenyl functional groups.
The combination of the use of the reinforcing mineral filler treated in a particular way, indicated above, and the use of one or more surfactants results in a polyaddition silicone material, especially one that can be used for taking impressions, providing a compromise between the following desired characteristics: fluidity (in the uncrosslinked state) and hydrophilicity (both in the uncrosslinked and the crosslinked state) and high mechanical properties (in the crosslinked state).